
\documentclass[a4paper]{article}
\usepackage{pgfplots}
\usepackage{pgfplots.assert}
    \pgfplotsset{compat=1.3}

\begin{document}

\pgfplotsset{contour/axes=yzx}

\makeatletter

\pgfplotsassertequalstok{z}{\pgfplotsplothandlercontour@axis@inv@x}{x inv}%
\pgfplotsassertequalstok{x}{\pgfplotsplothandlercontour@axis@inv@y}{y inv}%
\pgfplotsassertequalstok{y}{\pgfplotsplothandlercontour@axis@inv@z}{z inv}%

\end{document}
